We are continuing to examine the structure, organization, expression, and evolution of the crystallin genes of the eye lens. The single alpha A-crystallin gene has been cloned from chickens and has a generally similar exon-intron structure to that of the alpha A-crystallin gene from mice; the human alpha A-crystallin gene has also been cloned and partially characterized. Hybridization studies have demonstrated differentail temporal and spatial regulation of the delta- and various members of the beta-crystallin gene families in the developing chicken lens. The beta 35-crystallin cDNA and gene are being extensively characterized. since this is the most fiber cell specific crystallin in the chicken lens. Five gamma-crystallin cDNAs and one gamma-crystallin gene from the mouse have been sequenced. The results showed that the gamma-crystallin protein domains are encoded in separate exons, and that the greatest diversity among the gamma-crystallins is in the third structural motif of the polypeptides. The promopter of the mouse alpha A-crystallin gene has been used to drive the bacterial chloramphenicol acetyl transferase (CAT) gene in primary explants of transfected imbryonic chickens lens epithelia; initial tests indicate that at least 400 base pairs of 5' flanking sequences contribute to the tissue-specific expression of this gene. The promoter regions of the two linked delta-crystallin genes have been sequenced, transcribed in vitro and used to express the CAT gene in transfected lens cells. All experiments suggest approciable functional differences between these two similar genes. Characterization of the new turtle crystallin (tau-crystallin) raises the possibility that it is related to gamma-crystallin and that it represents the origins of this specialized avian and reptilian lens protein.